Method of producing diammonium phosphate



METHODOF PRODUCING DIAMMONIUM PHOSPHATE Filed Aug. 18, 1930 aww-5M ATTOP/VEY 30 In the accompanying -drawing I have shown ered to 100 C. or still' more and its concen- ,Platenterd Nov. *21, 1933 l h l y. ,I

Unirse STATES PATENTfloF/Fice METHOD OF PRODUCING DIAMMNIUM PHOSPHATE Markus Larsson, Berlin, Germany, assignor to Y Kunstdunge'r Patent Verwertungs-Aktienge sellschaft,` Glarus, Switzerland Application August 18, 1930, Serial No.` 475,914,

and in Srweden August 23, 192,9

3 claims.v (ci. ,2s-107) When diammonium` phosphate is produced byr and the phosphoric acid solution is, preferably, absorption of ammonia into a solution of phos- Vpreheated to the boiling point before the ammophoric acid or monoammonium phosphate convniacal steam is supplied thereto. The ammonia siderable quantities of heat are evolved the utiaccompanying the steam is absorbedv by the phos- 1 lization of which hitherto caused considerable phoric acid in the vessel Sto form monoammoni- 60' diiculties. If ammoniar is supplied to aconum phosphate While pure steam escapes from centrated solution of vphosphoric acidV or monothe vessel 3. Said steam may be utilized for the ammonium phosphate the solution is rapidly preheating of the phosphoricacid solution which heated to the boiling point and then the water later is to be used in the process, or for other is partly'evaporated at the continued absorption heating purposes. The reaction heat evolved so that the reaction heat is utilized for the conwhen the ammonia is absorbed by the phosphoric centration of the solution. As, however, a, conacid in the vessel 3 causes a partial evaporation centrated solution of diammonium phosphate has of the weak phosphoricacid solution and is thus a comparatively high ammonia pressure, a great also completely utilized. part of the ammonia supplied escapes together The quantity ofv ammoniavwhich escapes to- 70 with the escaping steam which causes losses of gether with the steam from the vessel 1 durammonia and makes the technical application of ing the time required for the conversion vof the the process impracticable. monoammonium phosphate in said' vessel into -This invention relates to amethod of prodiammonium phosphate is less than that reducing diammonium phosphate in which the required for the conversion of the phosphoric acidv 75 action heat is fully utilized for thev concentrain the vessel 3 into monoammonium phosphate. tion of the solutionwithout loss of ammonia. The It is, therefore, suitable to ysupply more ammonia. essential feature of the invention consists, chiefly, to the vessel 1 than is required for the producin this that the ammonia is absorbed in a boiling of diammonium phosphate. rThey excess of .1 ing solution of phosphoric acid or monoammoammonia passes then through the solution with- S0 nium phosphate until diammonium phosphate is out being absorbed and as the solution is hot` formed and that the escaping mixture of steam (about 110 to 115 C.) said excess of ammonia and ammonia is supplied to a solution of phoscarries away considerable quantities of steam phoric acid for the recovery of the ammonia. whereby the temperature of the solution is low-4.1.5

in Figs. 1 and 2 two embodiments of apparatus tration is increased. As diammonium phosphate for carrying out my improved process. is less soluble than monoammonium phosphate Referring to Fig. 1, 1 is a. saturation vessel at high temperatures a great part of the diam- 3 provided with an agitator, to which a concenmonium phOSpha@ OImed CrystallZeS out in the *.1

supplied from an evaporator 2. The solution is, solution either directly or after cooling in a vcenpreferably, heated to the boiling point already trifuge 4 whereupon the SOlid diammOniUm phOS- Vwhenintroduced in the vessel 1. To the vessel phate is dried at a moderate temperature while 1` ammonia is also supplied which at the first the mother liquor is returned to the vessel 1 49 stage of the process is absorbed practically com- OEether With the neXt Charge 0f monoammo- 95 pletely by the solution While steam escapes due num phosphate solution. to the heat evolved by the reaction. -When about When phosphoric acid obtained in the leaching the half of the monoammonium phosphate has vof phosphate rock and generally containing imbeen converted into diammonium phosphate the purities of iron, aluminium, calcium etc. is used in i absorption of the ammoniawill be less complete the process, said impurities are precipitated in 100 and the escaping steam contains an increasing the vessel 3 by the ammonia supplied. As said percentage'of ammonia. The escaping ammoniprecipitation takes place at the boiling point of acal steam is supplied to a vessel 3 containing a the solution a granulary precipitate is obtained weak phosphoric acid solution which for instance which can easily be separated from the solution. has been produced by the leaching of phosphate The separation may, preferably, be performed in 105 rock with sulphuric acid or another mineral acid a filter press 5 whereupon the clear solution of in presence of alkali sulphate. The quantity of monoammonium phosphate is supplied to the phosphoric acid in the vessel 3 is suited in such evaporator 2 for its concentration before it is manner that it corresponds to the'quantity of supplied to the saturation vessel 1.

trated solution of monoammonium phosphate is solution. The crystal mass is separated from the 90 y monoammonium phosphate used in the vessel 1 Asis clear from the above description the whole .110.

phorio acid solution obtained in leaching phosw phate rock is rst concentrated to a suitable strength in. an evaporator 6 and is then supplied` to the iirst of a series of absorption Vessels '7, 8, 9.. The ammonia gas is supplied to the last absorption vessel 9, in Which the solution is saturated to diarnrnonium phosphate. From the vessel 9 ammoniacal steam escapes which is conveyed `tlfn'ough,the vessels 8 and 7, wherein the am-y monia is completely absorbed and a further evaporation tastes piace. The steam 'escaping' from the vessel 7 is Vused yfor the preheating of the Weak phosphoric acid solution before the latter' is supplied to the evaporator 6, or forother heat-- ing purposes.

Aften-the zcontents.:V of the :vessels 9-.fhave been. neutralizedf. substantially to jdianmoniuzn phjos'- s phate; theo contents Varesupplied vtonacentrifuge :l0: ini-Which'1thefsolid crystal mass-isseparated.v iSaidu-yessel Ti "thenl'ledawithphosphoric acid solutionsfromzlthei evaporator.; and v,placed 'rstin the series of absorptionfvesselsgwhile ammoniay ""5 now isv.introduoedV intofthegvessel -yltowhichgalso the: mother liquor from thecontentsofi-'thevec rsel ggpreferablyris, supplied,` The :process is.` thus :continued until the cont'ents'jof the-vessel 8` have urated fto diam-moniumphosphate,- and "fuese-isf.; s Y l .Y The rrnethoolr of/ 'produoing'diarmnonium Toont-.amine :monoammolliumPhosphateSubstanphosphate' which` comprises preheating asolution' tially to its boiling point, introducing an excess tof gaseous ammonia into saidpreheated solution nntil the latter is saturated substantially to the stage of (NH4 2HPO4, supplying the escaping :mixture of ammonia and steam to a second solution lcontaining free phosphoric acid and being preheated gbeforehand substantially to its boiling point, and preheating phosphoric acid solution to be used in the continuous performance of the process by means of the steam escaping from the .second solution.

.2. 'The `'method of producing diarnmonium phosphate, Which comprises preheating a solution containing monoanimonium phosphate substantially Ator its boiling point, introducing gaseous ammonia into said solution, supplying the escaping mixture of arnmonia and steam to a second :solution containing free phosphoric acid and being preheated beforehand substantially to its alooiling point, the supply of ammonia being conltinued until the Inonoarnmonium phosphate of the rst-mentioned solution has been converted .substantially into diammpniurn phosphate and the phosphoric acid of the last-mentioned soluztionhas'been converted' substantially into mono- :'anlrnoniuzn phosphate, removing solid diaznn'lo-l y:niurn phosphate `from thefsolution of diarnrnonium phosphate produced, and mixingV there- -4,niazining motherliquorWiththe solutio zaamrnoniumgfphosphategproduoed jorj: us

continuous perforina ce of theproces .fheffmethoidav of ,reducingx daL phosphatewhich;comprisesintroduoin @cess'ofigaseousanunonia a boiling :containngmonoammonium effuntil he Y zlattei,issaturatedsubstantially.to the stageV `or 5i' rNHm-leomand. supplying ,the escaping.' s111111@- lniacal-steam: toa-second boiling: Solution-rechtsming free phosphoric acid'fthej: saidV solutions; being vl0efillfeihand?meileated substantal'lyfto*theirjioil- 115 ing :poiritzand fthe jhejat coveredi byl thaabsrption i? ofzltheaammoniaffrbeneremoved chey by be fsteamzlescapingfrom' saidsolutions.: i --1 UFMARKUS'ELARSEQN 

